Machines for the forming, filling and sealing of packages from a continuous web or film of material are well known in the art. These form, fill and seal packaging machines require a smooth and efficient means for advancing the film over the former in cooperation with the other parts of the system to insure that the film is properly formed into a tube, filled with product and sealed into individual packages.
In order to meet this requirement, the movement is usually imparted in one of two ways: (1) moving the clamping/sealing jaws, or (2) moving separate feed belts or rollers in engagement with the tube. Many package machinery users prefer the feed belt approach of the second category. Thus, considerable research and development is proceeding in this direction today. As shown in a relatively recent U.S. Pat. No. 4,288,965 to James, a pair of belts for advancing the film engage opposite sides of the film along a hollow mandrel that allows product delivery to the tube. The belts are driven through clutches connected to the main drive system of the machine. Such a belt film advancing system, however, is not without its disadvantages.
During the form, fill and seal machine operating cycle, the film advancing belts are intermittently driven. The belts are driven to advance the film a sufficient length for the forming of an individual package. The belts are then stopped during the sealing and cutting of the individual package from the film tube.
As should be appreciated, dynamic friction exists at the contact points between (1) the film advancing belts and the pulleys over which they extend and are driven, and (2) the belts and the packaging film being advanced. This friction produces heat that is accumulated in the pulleys and, more importantly, in the belts themselves. Each rapid acceleration and deceleration of the belts as described above for intermittent advance of the packaging film represents a change in directional forces promoting slipping between the belts, pulleys and packaging film. The resulting increased dynamic friction means increased heat that is accumulated in the belts.
Over extended periods of use, the stored heat may become great enough to induce some stretching in the belt. This stretching further promotes slippage of the belts with respect to the pulleys and, therefore, even more heat accumulation. Thus, it may be seen that frictional heat production and, therefore, the accumulation of heat in the belts increases exponentially to produce increased belt wear, inefficient feeding action and eventually a need to replace the belts.